1. Field of the Invention
The present invention relates to an active matrix type liquid crystal display device.
2. Related Art of the Invention
At present, simultaneous lighting image inspection of a liquid crystal display panel is performed in a cell process in order to improve the production efficiency and to reduce the production cost in the liquid crystal display device. The simultaneous lighting image inspection refers to simple image inspection to check the presence or absence of a luminescent spot or a line defect by such a way that, for example, when an entire screen is displayed, all pixels are simultaneously lighted by simultaneously connecting source wiring parts and gate wiring parts to common inspection switching elements, respectively, and by applying a same signal to the source wiring parts and the gate wiring parts.
The plurality of inspection switching elements used for the simultaneous lighting image inspection are formed beforehand as inspection thin-film transistors (hereinafter refer to as inspection TFTs), for example, in an array process of the liquid crystal display device. The inspection TFT is formed in a place where a drive IC of the liquid crystal display device is provided. The inspection TFT is formed between an inspection signal input pad and the source wiring part or the gate wiring part. Further, the inspection TFT controls switching elements in the pixels of a display area in a lump by applying an inspection signal input into the inspection signal input pad to the source wiring parts or the gate wiring parts (for example, see Japanese Patent Laid-Open No. 2000-155302).
The entire disclosure of Japanese Patent Laid-Open No. 2000-155302 is incorporated herein by reference in its entirety.
The operation of the inspection TFT will be described in detail with reference to FIG. 4.
FIG. 4 is a figure schematically showing a configuration of a part of a conventional color liquid crystal display device. The liquid crystal display device shown in FIG. 4 includes inspection TFTs 22 and 23, inspection signal input pads 24 to 26, and pixels 27 on an array substrate 21. The pixels 27 are arranged in a display area 30, and the other components are arranged in the area outside the display area. Note that in the liquid crystal display device shown in FIG. 4, common electrodes and common electrode inspection wiring part connected to the common electrodes are not shown.
In the following, a case of simultaneously lighting red pixels will be described as an example.
First, a control signal for turning on/off the inspection TFTs 22 and 23 is input into the inspection signal input pad 26. The control signal is applied to each gate of the inspection TFTs 22 and 23 via a common wiring part 35. Thereby, the inspection TFT 22 and 23 are made to turn on. Next, an inspection gate signal is input into an inspection signal input pad 25. Thereby, the inspection gate signal is applied to gate wiring parts 11a and 11b. 
Subsequently, an inspection source signal is input into the inspection signal input pad 24r.The control signal is already applied to the gate of the inspection TFT 22r, and hence the inspection TFT 22r is turned on. For this reason, the inspection source signal input into the inspection signal input pad 24r is applied to source wiring parts 12a and 12b. Thereby, all the red pixels 27r in the display area 30 are simultaneously lighted. Thus, disconnection of the source wiring part and the gate wiring part, breakdown of the switching element of the red pixels 27r, or the like, is recognized as a line defect or a luminescent spot, if present.
Similarly, when an inspection source signal is input into the inspection signal input pad 24g, it is possible to simultaneously light all of the green pixels 27g in the display area 30. Further, when an inspection source signal is input into the inspection signal input pad 24b, it is possible to simultaneously light the blue pixels 27b in the display area.
In this way, since a defective element can be detected by performing the simultaneous lighting image inspection in the cell process before expensive IC elements and the like are mounted, it is possible to improve the production efficiency and to reduce the production cost in the liquid crystal display device as a whole. Note that the simultaneous lighting image inspection method described with reference to FIG. 4 is an example. As another simultaneous lighting image inspection method, the inspection may also be performed in such a manner that the display area is divided into a plurality of areas, and the respective areas are simultaneously lighted. Further, all the pixels in the display area may also be simultaneously lighted.
However, in the manufacturing process of the liquid crystal display device, static electricity may be generated due to peeling charge, surge voltage, or the like. The inspection TFT is also capable of functioning as a capacitor having a capacitance larger than that of the switching element of the pixel in the display area, and hence easily accumulates static electricity. The static electricity accumulated in the inspection TFT becomes a cause of destruction of the inspection TFT, disconnection of wiring parts around the inspection TFT or the like.
In the conventional liquid crystal display device, there is taken a measure for preventing the switching element formed in the pixel inside the display area from being destroyed by the static electricity. However, the inspection TFT formed outside the display area is formed in a position away from the display area, and hence cannot receive the benefit of the measure against static electricity in the display area. Further, there is a problem that when destruction of the inspection TFT, disconnection of the wiring parts around the inspection TFT or the like is caused by the static electricity, it becomes impossible to perform the simultaneous lighting image inspection.
The present invention has been made in consideration of the above described problem, and an object of the invention is to provide a liquid crystal display device capable of reducing destruction of inspection switching elements or disconnection of wiring parts connected to the inspection switching elements, due to static electricity, as compared with conventional liquid crystal display devices.